If I understand correctly, you want to replace the search placeholder text with a custom value. You can actually do that with a custom filter function (similar to the previous solutions).
Add this custom code to the functions.php in your theme/child theme directory (copy from line 3 only!). Before editing, please make sure to have a full site back-up just in case!
Just change the $placeholder variable value on line 7 to anything you want it to.Best,
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